The present invention related generally to apparatus for lifting machinery and more particularly relates to safety lift apparatus for portable elevators.
Portable elevators have been used for many years as a convenient mechanism for transferring grain or other commodities from near ground level to the tops of graineries or other structures for filling bins therein. Until recently, most grain bins were not very high, and elevators for elevating the grain into those bins were of a manageable size. Consequently, a totally manual lift mechanism was satisfactory for raising the rear end of an elevator from a storage and transfer position near the ground to a position high above the ground over the top of a grain bin. A conventional manual lift mechanism for raising the rear end of the elevator included a pivotal attachment of the lower end of an elevator to a stationary carriage assembly and a strut pivotally attached to the stationary carriage assembly and extending into longitudinally movable contact with the elevator. A cable was connected to the strut on one end and onto a manually operated winch on the other end. By manually operating the winch to wind the cable around a reel, the strut was drawn longitudinally forwardly along the elevator resulting in raising the rear end of the elevator to the desired height.
In recent years, the use of much larger and higher grain bins plus the desire for grain elevators having much larger grain carrying capacities has resulted in the demand for significantly larger grain elevators which are both much longer and much larger and heavier than the elevators common in years past. Once set up, these longer and larger elevators are capable of transferring grain into higher bins at considerably increased rates; however, they are much more cumbersome and difficult to manipulate, position and set up. Therefore, it is desirable to utilize a power lift mechanism for raising the rear end of an elevator to the desired height over a grain bin, and it is preferable that such mechanisn be operable from the seat of a tractor or other vehicle to which the elevator is attached so that it can be simultaneously raised and moved backward into position over the grain bin. Indeed, some persons skilled in the art have substituted hydraulically powered winches on the ends of the lift cables in place of the conventional manual winches for raising elevators.
These powered systems, while basically accomplishing the purpose of making it more convenient to raise the elevator to the desired height, have also resulted in some significant problems. For example, the power lift can be safety hazard if operated by inexperienced or inattentive persons who allow the mechanism to lift the elevator to unsafe heights. The structure of the carriage and lift apparatus of most elevators is such that if the lift apparatus is allowed to travel too far, the center of gravity of the elevator may become positioned to the rear of the supporting apparatus causing the elevator to topple with the rear end falling to the ground from a considerable height while the front end suddenly vaults high into the air. Such a situation can occur without warning and can cause severe injury to persons near the elevator and severe structural damage to the elevator itself.
Also, because the grain bins for which such elevators are commonly used are quite high and the elevators become somewhat more unstable when raised to such heights, it is common practice, once the elevator is in position over the grain bin, to tie the upper end of the elevator to the top of the grain bin to anchor it to prevent it from tipping in case of high winds or other adverse conditions. Such a tie-down anchor, while being a considerable safety advantage to keep the elevator from tipping, also resists further raising of the rear end of the elevator. Therefore, if the operator should attempt to raise the elevator, for example, to remove the down spout of the elevator from the filler hatch on top of the bin, but forgets to unfasten the anchoring tie-down, severe structural damage could occur to both the elevator and the bin and could result in the elevator collapsing and injuring persons in the vicinity. While such an eventuality is unlikely with a manually operated winch because the operator could feel the resistance of the anchoring cable, it could quite easily happen with a powered winch. Consequently, the safety concern of most manufacturers as well as governmental regulations have generally inhibited the wide spread use of the more convenient power lift mechanisms on large elevators.
Another problem which has arisen from elevators equipped with power lift mechanisms is that while it is generally contemplated that a necessary power source such as a tractor with a hydraulic system for those mechanisms powered by hydraulic fluid will be available when the elevator is used, there are occasions in which a tractor with a hydraulic system is unavailable. Yet the operator may desire to operate the elevator with another vehicle such as a jeep or tractor which does not have the appropriate power source necessary to raise the elevator. In these circumstances, it is very desirable to be able to alternatively raise the elevator with manual means even though such manual raising means may not be as convenient as the powered lift means.